Prior work has suggested a model for age-related T cell failure in which T cells from aged mice show both altered surface glycoprotein patterns and defects in cytoskeleton-dependent relocalization of surface glycoproteins. In addition, OSGE, a protease specific for O-linked glycoproteins including CD43, CD44, and CD45, has been shown to restore function of aged T cells to levels similar to that of T cells of young donors. Three specific aims will address, respectively, (1) altered glycosylation, (2) cytoskeletal defects, and (3) repair of in vivo immune responses. Aim 1 a will use a battery of specific lectins and glycosidases to determine which T cell surface glycoproteins contribute to diminished synapse formation, calcium signals, and cytokine expression in aged T cells. Aim 1b will use 2D electrophoresis and glycan-profiling to identify the T cell surface glycoproteins whose susceptibility to enzymatic digestion parallels the ability of the enzymes to improve T cell function. Aim 1c uses a multiplex RT-PCR approach to develop a listing of age-related changes in mRNAs for glycosides and glycosyl-transferases. Aim 1 d evaluates specific surface glycoproteins, starting with CD44, CD45, CD4, and CDS, for susceptibility to the functionally relevant enzymes. Aim 2 will explore the molecular basis for the failure of aged T cells to move molecules either into the synapse, or into the distal pole complex (DPC) opposite from the site of APC contact. This aim explores two related hypotheses: (a) that T cell activation defects involve a failure to remove inhibitory molecules, including CD43 and protein phosphatases, from the synapse to the DPC, and (b) that the cytoskeletal defect involves altered phosphorylation of proteins in the ERM family. Aim 3 will use two in vivo adoptive transfer systems to see if enzyme-treated T cells from aged donors show improved function in responses to hapten-carrier conjugates and to transplantable tumors. Improved knowledge of the basis for poor T cell function in old age, and the mechanisms by which enzyme exposure corrects these defects, could point to new ways to protect the elderly from cancer and infection, as well as to improvements in vaccination methods for old people.